Varying the flexibility of the aromatic backbone in half sandwich rhodium(III) dithiolato complexes: A synthetic, spectroscopic and structural investigation

Abstract

A series of rhodium(III) half sandwich complexes of the type [Cp*Rh(PMe₃)(S–R–S)]; S–R–S = naphthalene-1,8-dithiolate, acenaphthene-5,6-dithiolate, [1,1’-biphenyl]-2,2’-dithiolate and [2,2’-binaphthalene]-1,1’-dithiolate are reported. In the case of [2,2’-binaphthalene]-1,1’-dithiolate, this represents an infrequent example of a metal complex containing this ligand. All the complexes have been fully characterised using multinuclear NMR spectroscopy and single-crystal X-ray diffraction. The single-crystal X-ray structure of the starting material [Cp*Rh(PMe₃)Br₂] (1) is also reported for the first time.

Keywords:

• dithiolates
• half sandwich
• complexation
• rhodium

Public Interest Statement

S,S′-bidentate ligands remain an important area of chemistry. Complexes bearing this type of ligand have a number of industrial applications including vulcanisation, lubricant additives and catalysis. In addition, S,S′-donors can support unusual magnetic properties and are important in biological systems This work describes the coordination of some simple bidentate S,S ligands to Iridium

1. Introduction

The coordination of S,S′-bidentate ligands remains an important area of chemistry. Complexes bearing this type of ligand have a number of industrial applications including vulcanisation (Bond & Martin, 1984; Burns & McAuliffe, 1979; Burns, McCullough, & McAuliffe, 1980; Eisenberg, 2007), lubricant additives (Phillips et al., 1995) and catalysis (Bond & Martin, 1984; Burns & McAuliffe, 1979; Burns et al., 1980; Eisenberg, 2007). In addition, S,S′-donors can support unusual magnetic properties (Tuna et al., 2012; Zhou, Wang, Wang, & Gao, 2011) and are important in biological systems (Woollins, 1996). As part of our interest in the properties of sulfur donor systems, we have investigated a series of dithiolate ligands bound to aromatic backbones of varying flexibility (Figure 1).

Figure 1. Dithiolate ligands studied in this work (charges omitted for clarity).

There has been little study on the coordination chemistry of these types of ligands compared to dithiolates such as benzene-1,2-dithiolate or ethane-1,2-dithiolate. One of the most notable exceptions to this was a series of publications by Teo and co-workers in the late 1970s and early 1980s (Teo, Bakirtzis, & Snyder-Robinson, 1983; Teo & Snyder-Robinson, 1978, 1979a, 1979b, 1981, 1984; Teo, Wudl, Hauser, & Kruger, 1977; Teo, Wudl, Marshall, & Kruger, 1977). They investigated the oxidative addition of the structurally related compounds tetrathionaphthalene (TTN), tetrachlorotetrathionaphthalene (TCTTN) and tetrathiotetracene (TTT) (Figure 2) to a variety of low-valent metal centres. With the work focusing on the extensive redox chemistry associated with these “non-innocent” ligands and their potential use as organic solid-state conductors (Teo & Snyder-Robinson, 1978, 1979a, 1979b, 1981, 1984; Teo, Wudl, Hauser, et al., 1977; Teo, Wudl, Marshall, 1977, Teo et al., 1983). Another interesting system bearing the related hexachlorodithionaphthalene (HCDTN) (Figure 2) resulted in an unusual trinuclear nickel complex [Ni₃(PPh₃)₃(S₂C₁₀Cl₆)₃] with the HCDNT acting as a bridging ligand (Bosman & van der Linden, 1977).

Figure 2. Structurally related aromatic sulfur donating ligands.

Some of the most recent work involving derivatives of naphthalene-1,8-dithiolate (A) has been in designing [FeFe]-hydrogenase mimics for the production of hydrogen, by both electrochemical and photochemical processes (Figure 3) (Figliola, Male, Horswell, & Grainger, 2015; Figliola et al., 2014; Samuel, Co, Stern, & Wasielewski, 2010; Wright, Lim, & Tilley, 2009). Complexes involving [1,1’-biphenyl]-2,2’-dithiolate (C) bound to iron have also been investigated as electron transfer catalysts designed to mimic iron hydrogenases (Figure 3) (Albers et al., 2014; Ballmann, Dechert, Demeshko, & Meyer, 2009; Charreteur et al., 2010). The coordination chemistry of the structurally related ligand acenaphthene-5,6-dithiolate (B) has received very little investigation out with our own research. (Topf, Monkowius, and Knör (2012) used the acenaphthene backbone as a linker between a 1,2-diimine unit and a dithiolate binding site. The iron carbonyl complex formed using this ligand showed potential as a multielectron transfer photosensitiser for artificial photosynthesis and as a bio-inspired photoredox catalyst (Figure 3).

Figure 3. Iron-based catalysts based on A (left), B (centre) and C (right).

Figure 4. The section of the ¹H NMR spectrum of 2c showing the four pseudo triplet of doublets with a splitting diagram showing how these signals are formed.

Figure 5. Crystal structures of 1 (Top), 2a (Middle left), 2b (Middle right), 2c (Bottom left) and 2d (Bottom right). Hydrogen atoms are omitted from all structures for clarity. Ellipsoids are plotted at the 50% probability level.

Beyond the electron transfer mimics, there are few examples of complexes incorporating ligand C. Two molybdenum complexes have been reported with one containing an Mo oxygen triple bond (Conry & Tipton, 2001; McNaughton, Tipton, Rubie, Conry, & Kirk, 2000). In addition, two methods to synthesise titanocene-2,2’-dithiolatobiphenyl have been published (Aucott et al., 2005; Stafford, Rauchfuss, Verma, & Wilson, 1996). The 2,2’-binaphthalene-based ligand, D, has been largely overlooked with regards to its complexation chemistry compared to the 1,1’-binaphthalene derivative. The only work reported involving this ligand thus far has been its preparation by Armarego (1960), the single-crystal X-ray structure (Kempe, Sieler, Hintzsche, & Schroth, 1993), one titanium complex (Aucott et al., 2005) and a platinum complex (Aucott, Kilian, Robertson, Slawin, & Woollins, 2006).

We have recently published two papers investigating the use of ligands A-C in the formation of half sandwich rhodium and iridium complexes (Nejman, Morton-Fernandez, Black, et al., 2015; Nejman, Morton-Fernandez, Moulding, et al., 2015). This paper describes the synthesis of a further four half sandwich rhodium (III) dithiolato complexes bearing a neutral phosphine donor. In this contribution, a different phosphine donor has been used compared to the previous work (trimethylphosphine instead of triethylphosphine) (Nejman, Morton-Fernandez, Black, et al., 2015). Additionally, a new ligand has been investigated [2,2’-binaphthalene]-1,1’-dithiolate (D). Two synthetic methods were employed due to the varying difficulty in preparing the ligand precursors. Both of these methods were different to the procedures used within our previous work (Nejman, Morton-Fernandez, Black, et al., 2015; Nejman, Morton-Fernandez, Moulding, et al., 2015). Furthermore, the single-crystal X-ray structure of the complex precursor, [Cp*Rh(PMe₃)Br₂] (1), is reported for the first time. All the complexes have been fully characterised, principally by multinuclear NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction.

2. Results and discussion

2.1. Synthetic methods

The dithiol pro-ligands [Naphth(SH)₂] (H₂a), [Acenap(SH)₂] (H₂b) and [Biphen(SH)₂] (H₂c) were prepared from their respective disulphides, naphtho[1,8-cd]-1,2-dithiole (Ashe, Kampf, & Savla, 1994), 5,6-dihydroacenaphtho[5,6-cd]-1,2-dithiole (Benson et al., 2013) and dibenzo[c,e]-1,2-dithiine (Cossu, Delogu, Fabbri, & Maglioli, 1991). The reduction of the disulphides was performed using NaBH₄ followed by an acidic work up which afforded the three pro-ligands (Figure 6) (Yui, Aso, Otsubo, & Ogura, 1988). The disulphide precursor to D, [2,2’-BinapS₂], was prepared according to the literature procedure by Armarego (1960). The reduction to the dithiol was not attempted as the amount of disulphide prepared was not sufficient. For this reason, the reduction to the reactive dithiolate was performed in situ using lithium triethylborohydride.

Figure 6. Synthesis of the pro-ligands H₂a-c.

The synthesis of [Cp*Rh(PMe₃)(NaphthS₂)] (2a), [Cp*Rh(PMe₃)(AcenapS₂)] (2b), [Cp*Rh(PMe₃)(BiphenS₂)] (2c) and [Cp*Rh(PMe₃)(2,2’-BinapS₂)] (2d) is shown in Figure 7. The metathesis of the bromide ligands with dithiolates A-D proceeds smoothly at room temperature. The presence of the phosphine group allowed the reaction progress to be monitored by ³¹P NMR spectroscopy. In the case of 2a-c, this meant the loss of the signal from 1, whilst for 2d, the product and 1 are soluble in THF so the conversion could be observed. Upon completion of the reaction for 2a-c filtration of the precipitate followed by washing with methanol was sufficient to afford pure compound. For 2d, purification by column chromatography was required (silica/CH₂Cl₂). Excellent isolated yields of between 82 and 91% were obtained after purification. Compared to the similar complexes incorporating triethylphosphine, this represents an increase in the isolated yield of approximately 10% (Nejman, Morton-Fernandez, Black, et al., 2015). The synthesis of 2a-d all proceeded via a reactive dithiolate intermediate, whereas the triethylphosphine derivatives were prepared by reacting H₂a-c directly with the dichloro rhodium precursor. The dithiols represent a less reactive sulfur centre which could explain the higher yields obtained for the complexes reported here.

Figure 7. Reaction conditions for the preparation of 2a-d.

2.2. Data analysis

The ¹H NMR spectra (CDCl₃) for 2a and 2b show the expected signals, with splitting, from the aromatic backbones in the range of 7.88–6.91 ppm. In the case of 2c and 2d, we observe 8 and 10 signals, respectively, as the two joined aryl ring systems are inequivalent. This is due to the inability of the ligand backbones to rotate around the aryl–aryl bond. Four of the aromatic signals observed for 2c appear as a pseudo triplet of doublets instead of the expected doublet of doublet of doublets. This is due to the ³J_HH coupling constants observed between H_b and H_a as well as H_b and H_c (Figure 4) being almost identical. Two of these signals overlap closely (δ_H 7.19 and 7.18 ppm, Figure 4); however, both can be distinctly observed and the coupling constants easily extracted. These observations mirror those made for other similar rhodium complexes we have prepared incorporating ligands A-C (Nejman, Morton-Fernandez, Black, et al., 2015). For 2d, this signal is not observed as the equivalent positions from each of the two naphthalene ring systems overlap resulting in multiplets. The η⁵–Cp* methyl signals range from 1.58 to 1.42 ppm and are split into doublets by long range phosphorus coupling (⁴J_Hp = 3.0–3.2 Hz). The signals from the methyl groups attached to the phosphorus atom appear as a doublet of doublets for 2a-c, with ³J_HP coupling (³J_Hp = 10.3–10.5 Hz) and long range ⁴J_HRh coupling (⁴J_HRh = 0.6–0.7 Hz). Only a doublet is observed for this signal in 2d with a similar ³J_HP coupling to that seen in complexes 2a-c.

The ³¹P{¹H} NMR spectra (CDCl₃) for 1 and 2a-d are shown in Table 1. Complexes 2a-d all display an upfield shift in the ³¹P{¹H} NMR spectra compared to the starting material 1 (Δδ = 0.7–3.3 ppm). The coordination of the dithiolate ligand is also accompanied by a small increase in the ¹J_PRh coupling (Δ¹J_PRh = 11–15 Hz) in 2a-d when compared to 1. Both of these observations match those made in the ³¹P{¹H} NMR spectra of the triethylphosphine derivatives of 2a-c (Nejman, Morton-Fernandez, Black, et al., 2015).

Table 1. ³¹P{¹H} NMR data (CDCl₃) for 1 and 2a-d. All δ values are in ppm and J values are in hertz

	1^†	2a	2b	2c	2d
δP	3.6	1.7	2.9	0.3	2.2
^1JPRh	137	150	148	153	152

^† Values obtained from a sample run on a Bruker Avance II 400 NMR spectrometer (162 Hz).

As expected, the ¹³C{¹H} NMR spectra (CDCl₃) of 2a-d mirrors that of the ¹H NMR spectra, with distinct signals for all carbons in the biphenyl and binaphthyl examples. Interestingly, only one of the quaternary carbons bound to the sulfur atoms is split into a doublet (³J_Cp = 6.5 Hz (2c) and 6.7 Hz (2d)) by the phosphorus atom in 2c and 2d. This provides further support of the difference between the two sides of the aryl–aryl bond. The mass spectra of 2a-d each showed a peak corresponding to [M–PMe₃ + H]⁺ ions at m/z 429, 455, 455 and 555, respectively. Homogeneity of the complexes 2a-d was confirmed by means of accurate elemental analysis.

2.3. Single-crystal X-ray diffraction

Despite the previously reported synthesis and spectroscopic characterisation of precursor complex 1 (Jones & Feher, 1984), its single-crystal X-ray data have not been published. Therefore, for completeness we include it here. The crystal structures of 1 and 2a-d are shown below in Figure 5 with selected structural parameters in Tables 2 and 3.

Table 2. Selected bond lengths [Å] and angles [°] for 1

	1
Rh1–P1	2.284(2)
Rh1–Br1	2.529(1)
Rh1–Br2	2.550(1)
P1–Rh1–Br1	87.14(3)
P1–Rh1–Br2	86.91(3)
Br1–Rh1–Br2	94.82(2)

Table 3. Selected bond lengths [Å], angles [°] and displacements [Å] for 2a-d

	2a	2b	2c	2d
Rh1–P1	2.284(1)	2.272(2)	2.2773(9)	2.2851(8)
Rh1–S1	2.331(1)	2.330(2)	2.3691(8)	2.3677(7)
Rh1–S9	2.332(1)	2.330(2)
Rh1–S12			2.3705(8)
Rh1–S20				2.3994(8)
P1–Rh1–S1	89.85(5)	87.02(3)	88.79(3)	96.29(3)
P1–Rh1–S9	84.87(5)	87.37(4)
P1–Rh1–S12			91.27(3)
P1–Rh1–S20				84.11(3)
S1–Rh1–S9	85.41(5)	87.78(3)
S1–Rh1–S12			93.94(3)
S1–Rh1–S20				95.00(3)
Splay angle^a	19.2(5)	21.0(3)
Torsion angles
S1–C1···C9–S9	8.9(3)	5.2(2)
C1–C10–C5–C6	177.5(6)	178.5(3)
C9–C10–C5–C4	178.1(6)	177.3(3)
C1–C6–C7–C12			68.0(4)
C1–C10–C11–C20				79.0(4)
Out of plane displacements
S1	0.213	0.117	0.184	0.189
S9	0.149	0.121
S12			0.003
S20				0.086

^a Calculated as [(S1–C1–C10)+(C1–C10–C9)+(C10–C9–S9)−360].

All of the complexes, 1 and 2a-d, adopt the piano stool geometry around the rhodium centre we have seen previously (Nejman, Morton-Fernandez, Black, et al., 2015; Nejman, Morton-Fernandez, Moulding, et al., 2015). The η⁵–Cp* ring in 1 is slightly tilted as the Rh–C bond lengths vary from 2.141(4) to 2.252(4) Å. The Rh–Br bond lengths (2.550(1) and 2.529(1) Å) and Rh–P bond length (2.284(2) Å) are similar to those previously reported within the Cambridge Structural Database for compounds of a similar type (Rh–Br; 2.543 Å, Rh–P; 2.288 Å) (Bruno et al., 2002; Macrae et al., 2008; Thomas et al., 2010). The angles around the rhodium centre vary with the two P–Rh–Br angles being below the idealised 90°. This is accompanied by a widening of the Br–Rh–Br angle to 94.82(2)° as the two larger atoms try and sit further apart.

The Rh–S bond lengths of 2a and 2b were almost identical (2a; 2.331(1) and 2.332(1) Å, 2b; 2.330(2) Å), whilst in 2c and 2d there was more variation and they were slightly longer (2c; 2.3691(8) and 2.3705(8) Å, 2d; 2.3677(7) and 2.3994(8) Å). These are comparable to other half sandwich complexes with Rh–S bonds reported by ourselves and Jin and co-workers ranging from 2.340 to 2.386 Å (Nejman, Morton-Fernandez, Black, et al., 2015; Wang, Lin, Blacque, Berke, & Jin, 2008; Xiao & Jin, 2008; Yao, Xu, Huo, & Jin, 2013). The Rh–P bond lengths show no appreciable change compared to 1 with little variation across the series of 2a-d.

All of the non-Cp* angles around the rhodium centre are reduced to less than 90° for 2a and 2b. This is a consequence of the rigid ligand backbone preventing the sulfur atoms from adopting a more ideal geometry. The effect is most obvious for the naphthalene system as the peri positions are restricted to a slightly shorter distance than those in the acenaphthene system. For both 2a and 2b, the splay angles are large and positive (2a; 19.2(5)°, 2b; 21.0(3)°) as the rhodium centre forces the sulfur atoms apart. The S1–C1···C9–S9 torsion angle is larger in 2a than 2b, again as a consequence of the more limited movement of the sulfur atoms imposed by the backbone. The central C–C–C–C torsion angles are similar in both complexes showing limited buckling of the ring system. The out of plane displacement of the sulfur atoms is slightly greater in 2a than 2b.

In complexes 2c and 2d the non-Cp* angles show a broader range than in 2a and 2b ranging from 88.79(3)–93.94(3)° to 84.11(3)–96.29(3)°, respectively. The ability of the backbone to twist around the aryl–aryl bond allows the sulfur atoms to adopt a more idealised geometry. The torsion angle between the two aryl rings is larger in 2d (79.0(4)°) than 2c (68.0(4)°) most likely due to the added steric bulk of having a binaphthyl instead of biphenyl-based system. In both 2c and 2d, the out of plane displacement of the sulfur atoms are similar.

3. Conclusions

We have prepared and fully characterised a series of new rhodium(III) η⁵–e have prepared and fully characterised a series of new rhodium(III) ηad ₃)Br₂] with a series of dithiolates attached to aromatic backbones. Similar features were seen in both the NMR spectra and single-crystal X-ray structures compared to previous rhodium complexes incorporating ligands A-C we have reported (Nejman, Morton-Fernandez, Black, et al., 2015; Nejman, Morton-Fernandez, Moulding, et al., 2015). The work herein clearly demonstrates the utility of these sulfur ligands in organometallic complexes, with complexes of this type having potential uses in the formation of multimetallic systems.

4. Experimental

4.1. General

Unless otherwise stated all manipulations were performed under an oxygen-free nitrogen atmosphere using standard Schlenk techniques and glassware. Solvents were collected from an MBraun Solvent Purification System or dried and stored according to common procedures (Armarego & Chai, 2009). [Cp*Rh(PMe₃)Br₂] was prepared following literature procedures (Ojima, Vu, & Bonafoux, 2002). The disulphide ligand precursors were made according to literature methods (Armarego, 1960; Ashe et al., 1994; Benson et al., 2013; Cossu et al., 1991). The pro-ligand H₂a was prepared following the literature procedure (Yui et al., 1988), with H₂c prepared following an identical procedure. H₂b was prepared according to literature (Nejman, Morton-Fernandez, Black, et al., 2015). ¹H, ¹³C{¹H}, ³¹P and ³¹P{¹H} NMR spectra were obtained on either a Bruker Avance II 400 or Bruker Avance III 500 spectrometer. Full assignments of the ¹H and ¹³C{¹H} NMR spectra were made with the aid of H–H DQF COSY, H–C HSQC and H–C HMBC experiments. For ¹H and ¹³C{¹H} spectra δ_H and δ_C are reported relative to TMS, residual solvent peaks (CDCl₃; δ_H 7.26, δ_C 77.2 ppm) were used for calibration. For ³¹P and ³¹P{¹H} spectra δ_P are reported relative to external 85% H₃PO₄. All measurements were performed at 21°C with shifts reported in ppm. p-td has been used to denote a pseudo-triplet of doublet. IR spectra were collected on a Perkin Elmer 2000 NIR/Raman Fourier transform spectrometer with a dipole pumped NdYAG near-IR excitation laser. Mass spectra were acquired by the EPSRC UK National Mass Spectrometry Facility at Swansea University. Elemental analysis was performed by Stephen Boyer at the London Metropolitan University.

4.2. Dithiolato complexes

4.2.1. [Cp*Rh(PMe₃)(NaphthS₂)] (2a)

A methanol (20 mL) solution of [Cp*Rh(PMe₃)Br₂] (120 mg, 0.25 mmol), [Naphth(SH)₂] (60 mg, 0.31 mmol) and NaOMe (17 mg, 0.31 mmol) was stirred at room temperature overnight. The red precipitate was filtered, washed with MeOH then dried under vacuum for 3 h. The product was obtained as a red solid (110 mg, 0.21 mmol, 83%). Crystals suitable for X-ray work were obtained by slow evaporation from CH₂Cl₂. Anal. calcd. for C₂₃H₃₀PRhS₂ (504.06 g mol⁻¹): C, 54.76; H, 5.99. Found: C, 54.69; H, 5.96. ¹H NMR (400 MHz, CDCl₃): δ 7.88 (dd, ³J_HH = 7.3, ⁴J_HH = 1.3 Hz, 2 H, H2,8), 7.47 (dd, ³J_HH = 8.1, ⁴J_HH = 1.1 Hz, 2 H, H4,6), 7.05 (dd, ³J_HH = 8.1 & 7.3 Hz, 2 H, H3,7), 1.54 (dd, ²J_Hp = 10.3, ³J_HRh = 0.7 Hz, 9 H, PMe₃), 1.49 (d, ⁴J_Hp = 3.0 Hz, 15 H, Cp*–Me). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 139.5 (d, ³J_Cp = 5.4 Hz, C_q, C1,9), 136.3 (C_q, C5), 133.9 (C_q, C10), 128.1 (CH, C2,8), 124.9 (CH, C4,6), 123.8 (CH, C3,7), 99.7 (dd, ¹J_CRh = 4.5, ²J_Cp = 2.9 Hz, C_q, Cp*), 14.9 (d, ¹J_Cp = 32.7 Hz, CH₃, PMe₃), 8.9 (CH₃, Cp*). ³¹P NMR (162 MHz, CDCl₃): δ 1.7 (br d, ¹J_PRh = 149 Hz). ³¹P{¹H} NMR (162 MHz, CDCl₃): δ 1.7 (d, ¹J_PRh = 150 Hz). HRMS (APCI+): m/z (%) Calcd. for C₂₀H₂₂RhS₂: 429.0212, found 429.0209 (100) [M–PMe₃ + H]. IR (KBr): ν_max/cm⁻¹ 3040w (ν_Ar-H), 2907 m (ν_C-H), 1536s, 1195 m, 952s, 810 m, 761 m.

4.2.2. [Cp*Rh(PMe₃)(AcenapS₂)] (2b)

A methanol (20 mL) solution of [Cp*Rh(PMe₃)Br₂] (120 mg, 0.25 mmol), [Acenap(SH)₂] (68 mg, 0.31 mmol) and NaOMe (17 mg, 0.31 mmol) was stirred at room temperature overnight. The red precipitate was filtered, washed with MeOH then dried under vacuum for 3 h. The product was obtained as a red solid (121 mg, 0.22 mmol, 91%). Crystals suitable for X-ray work were obtained by slow evaporation from CH₂Cl₂. Anal. calcd. for C₂₅H₃₂PRhS₂ (530.07 g mol⁻¹): C, 56.60; H, 6.08. Found: C, 56.49; H, 6.11. ¹H NMR (400 MHz, CDCl₃): δ 7.77 (d, ³J_HH = 7.2 Hz, 2 H, H2,8), 6.91 (d, ³J_HH = 7.2 Hz, 2 H, H3,7), 3.17 (s, 4 H, H11,12), 1.54 (dd, ²J_Hp = 10.3, ³J_HRh = 0.7 Hz, 9 H, PMe₃), 1.50 (d, ⁴J_Hp = 3.0 Hz, 15 H, Cp*–Me). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 141.7 (C_q, C4,6), 141.1 (C_q, C5), 134.8 (d, ²J_CRh = 5.5 Hz, C_q, C1,9), 132.3 (C_q, C10), 128.6 (CH, C2,8), 117.9 (CH, C3,7), 99.5 (dd, ¹J_CRh = 4.9, ²J_Cp = 2.9 Hz, C_q, Cp*), 30.1 (CH₂, C11,12), 15.0 (d, ¹J_Cp = 33.0 Hz, CH₃, PMe₃), 8.9 (CH₃, Cp*). ³¹P NMR (162 MHz, CDCl₃): δ 2.9 (br d, ¹J_PRh = 148 Hz). ³¹P{¹H} NMR (162 MHz, CDCl₃): δ 2.9 (d, ¹J_PRh = 148 Hz). HRMS (APCI+): m/z (%) Calcd. for C₂₂H₂₄RhS₂: 455.0369, found 455.0362 (80) [M–PMe₃ + H], 216.0060 (95) [C₁₂H₈S₂], 184.0339 (55) [C₁₂H₈S], 152.0618 (100) [C₁₂H₈]. IR (KBr): ν_max/cm⁻¹ 3037w (ν_Ar-H), 2907 m (ν_C–H), 1552 m, 1404 m, 1027 m, 952s, 837 m, 734 m.

4.2.3. [Cp*Rh(PMe₃)(BiphenS₂)] (2c)

A methanol (20 mL) solution of [Cp*Rh(PMe₃)Br₂] (120 mg, 0.25 mmol), [Biphen(SH)₂] (71 mg, 0.33 mmol) and NaOMe (19 mg, 0.33 mmol) was stirred at room temperature overnight. The red precipitate was filtered, washed with MeOH then dried under vacuum for 3 h. The product was obtained as a red solid (110 mg, 0.21 mmol, 83%). Crystals suitable for X-ray work were obtained by slow evaporation from CH₂Cl₂. Anal. calcd. for C₂₅H₃₂PRhS₂ (530.07 g mol⁻¹): C, 56.60; H, 6.08. Found: C, 56.49; H, 6.15. ¹H NMR (400 MHz, CDCl₃): δ 7.66 (dd, ³J_HH = 7.6, ⁴J_HH = 1.3 Hz, 1 H, H2), 7.64 (dd, ³J_HH = 7.7, ⁴J_HH = 1.3, 1 H, H11), 7.19 (p-td, ³J_HH = 7.5, ⁴J_HH = 1.4 Hz, 1 H, H4), 7.18 (p-td, ³J_HH = 7.6, ⁴J_HH = 1.4 Hz, 1 H, H9), 7.03 (p-td, ³J_HH = 7.6, ⁴J_HH = 1.6 Hz, 1 H, H3), 6.98 (p-td, ³J_HH = 7.6, ⁴J_HH = 1.6 Hz, 1 H, H10), 6.94 (dd, ³J_HH = 7.5, ⁴J_HH = 1.5 Hz, 1 H, H5), 6.86 (dd, ³J_HH = 7.5, ⁴J_HH = 1.5 Hz, 1 H, H8), 1.58 (d, ⁴J_Hp = 3.2 Hz, 15 H, Cp*–Me), 1.39 (dd, ²J_Hp = 10.5, ³J_HRh = 0.6 Hz, 9 H, PMe₃). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 151.0 (C_q, C6), 150.0 (C_q, C7), 143.0 (d, ³J_Cp = 6.5 Hz, C_q, C1), 140.2 (C_q, C12), 137.2 (CH, C2), 135.2 (CH, C11), 130.9 (CH, C8), 130.6 (CH, C5), 126.2 (CH, C3,9), 125.7 (CH, C4), 125.5 (CH, C10), 99.3 (dd, ¹J_CRh = 5.3, ²J_Cp = 3.2 Hz, C_q, Cp*), 15.9 (d, ¹J_Cp = 31.6 Hz, CH₃, PMe₃), 8.8 (CH₃, Cp*). ³¹P NMR (162 MHz, CDCl₃): δ 0.3 (br d, ¹J_PRh = 153 Hz). ³¹P{¹H} NMR (162 MHz, CDCl₃): δ 0.3 (d, ¹J_PRh = 152 Hz). MS (APCI+): m/z (%) Calcd. for C₂₂H₂₄RhS₂: 455.0369, found 455.0365 (100) [M–PMe₃ + H]. IR (KBr): ν_max/cm⁻¹ 3037w (ν_Ar-H), 2905 m (ν_C-H), 1451 m, 1404 m, 1280w, 959s, 750s.

4.2.4. [Cp*Rh(PMe₃)(2,2’-BinapS₂)] (2d)

To a THF (15 mL) solution of [2,2’-BinapS₂] (117 mg, 0.37 mmol) was added lithium triethylborohydride (0.80 mL, 0.80 mmol, 1 M solⁿ in THF) at room temperature. The reaction was left to stir for 0.5 h during which time the solution turned from yellow to almost colourless. To this was added [Cp*Rh(PMe₃)Br₂] (148 mg, 0.31 mmol) and the solution turned instantly to a very dark red/purple colour. The reaction was left to stir at room temperature overnight. The solvent was removed under vacuum and the crude product purified by column chromatography (silica/CH₂Cl₂). The solvent was removed to afford the product as a dark purple solid (147 mg, 0.23 mmol, 82%). Crystals suitable for X-ray work were obtained by slow evaporation from CH₂Cl₂. Anal. calcd. for C₃₃H₃₆PRhS₂ (630.11 g mol⁻¹): C, 62.84; H, 5.75. Found: C, 62.73; H, 5.66. ¹H NMR (500 MHz, CDCl₃): δ 9.20 (d, ³J_HH = 8.6 Hz, 1 H, H3), 9.17 (d, ³J_HH = 8.5 Hz, 1 H, H18), 7.80 (d, ³J_HH = 8.3 Hz, 1 H, H6), 7.77 (d, ³J_HH = 8.2 Hz, 1 H, H15), 7.65 (d, ³J_HH = 8.3 Hz, 1 H, H13), 7.64 (d, ³J_HH = 8.2 Hz, 1 H, H8), 7.54–7.48 (m, 2 H, H4,17), 7.45–7.39 (m, 2 H, H5,16), 7.01 (d, ³J_HH = 8.3 Hz, 1 H, H9), 6.86 (d, ³J_HH = 8.3 Hz, 1 H, H12), 1.42 (d, ⁴J_Hp = 3.2 Hz, 15 H, Cp*–Me₃), 1.31 (d, ²J_Hp = 10.6 Hz, 9 H, PMe₃). ¹³C{¹H} NMR (125 MHz, CDCl₃): δ 150.1 (C_q, C11), 148.1 (C_q, C10), 140.8 (d, ³J_Cp = 6.7 Hz, C_q, C1), 138.3 (C_q, C2), 138.0 (C_q, C19), 137.5 (C_q, C20), 132.9 (C_q, C14), 132.1 (C_q, C7), 129.5 (CH, C12), 129.2 (CH, C3,9), 128.0 (CH, C15), 127.9 (CH, C18), 127.7 (CH, C6), 125.4 (CH, C17), 125.0 (CH, C13), 124.8 (CH, C8,16), 124.7 (CH, C5), 124.3 (CH, C4), 99.7 (dd, ¹J_CRh = 5.5, ²J_Cp = 3.5 Hz, C_q, Cp*), 15.7 (d, ¹J_Cp = 31.5 Hz, CH₃, PMe₃), 9.2 (CH₃, Cp*). ³¹P NMR (202 MHz, CDCl₃): δ 2.2 (br d, ¹J_PRh = 152 Hz). ³¹P{¹H} NMR (202 MHz, CDCl₃): δ 2.2 (d, ¹J_PRh = 152 Hz). HRMS (APCI+): m/z (%) Calcd. for C₃₀H₂₈RhS₂: 555.0687, found 555.0729 (90) [M–PMe₃ + H], 284.0738 (100) [C₂₀H₁₂S]. IR (KBr): ν_max/cm⁻¹ 3044w (ν_Ar-H), 2906 m (ν_C-H), 1493 m, 1281 m, 949s, 815s, 747s, 672 m, 546w.

4.3. Crystal structure analysis

Tables 4 and 5 list the details of data collections and refinements. Data for 1, 2b, 2c and 2d were collected using a Rigaku SCX-Mini (Mo–Kα, graphite monochromator) at −100°C; for 2b using a Rigaku Saturn724 at −148°C. Intensities were corrected for Lorentz polarisation, and adsorption. Structures were solved by direct methods and refined by full-matrix least-squares against F² (SHELXL) (Sheldrick, 2008). Hydrogen atoms were assigned riding isotropic displacements parameters and constrained to idealised geometries. Non-hydrogen atoms were refined anisotropically. CCDC No. 1489639–1489643.

Table 4. Crystallographic data for complexes 1, 2a and 2b

	1	2a	2b
Empirical formula	C13H24Br2PRh	C23H30PRhS2	C25H32PRhS2
M	474	504	530
Crystal system	Tetragonal	Orthorhombic	Monoclinic
Space group	P43212	P212121	P21/n
a [Å]	11.994(9)	8.2099(19)	8.265(7)
b [Å]	11.994(9)	13.649(3)	8.706(7)
c [Å]	23.274(19)	19.602(4)	32.87(3)
α [°]	90.0	90.0	90.0
β [°]	90.0	90.0	95.663(7)
γ [°]	90.0	90.0	90.0
V [Å^3]	3348(4)	2196.5(8)	2354(3)
Z	8	4	4
ρcalcd (g. cm^−3)	1.881	1.525	1.497
μ [cm^−1]	58.817	10.448	9.791
Measured refln.	30194	29827	22775
Unique refln.	3088	4016	5378
R [I>2σ(I)]	0.0186	0.0291	0.0378
wR	0.0344	0.0689	0.0981

Table 5. Crystallographic data for complexes 2c and 2d

	2c	2d
Empirical formula	C25H32PRhS2	C33H36PRhS2
M	530	630
Crystal system	Orthorhombic	Monoclinic
Space group	P212121	P21/c
a [Å]	9.5411(15)	10.4996(7)
b [Å]	15.202(3)	22.0450(15)
c [Å]	16.6474(19)	13.3815(9)
α [°]	90.0	90.0
β [°]	90.0	107.216(4)
γ [°]	90.0	90.0
V [Å^3]	2414.6(7)	2958.6(4)
Z	4	4
ρcalcd (g. cm^−3)	1.459	1.416
μ [cm^−1]	9.545	7.918
Measured refln.	25505	25373
Unique refln.	5526	5437
R [I>2σ(I)]	0.0189	0.0277
wR	0.0454	0.0725

Additional information

Funding

Funding. The authors received no direct funding for this research.

Notes on contributors

J. Derek Woollins

J. Derek Woollins has a long-standing interest in the synthetic and structural chemistry of group 16 elements and their coordination compounds. Recent work has investigated peri substituted naphthalenes and related systems, and the work described here examines the coordination of some peri and related ligand systems.